Generally, in a manufacturing process of a semiconductor integrated circuit, various processes, such as a film deposition process, an etching process or an oxidation-diffusion process, are repeatedly performed with respect to a semiconductor wafer, which is an object to be processed. In such kinds of processes, in a case in which there is no element or arrangement or member that receives a thermal damage in a wafer such as a case in which an oxidation film is deposited on a bare wafer, there is no problem if a heat treatment is performed at a high temperature of, for example, 800° C. to 900° C. However, for example, when an interlayer insulating film or the like is formed to make a circuit element to be multilayer, there is a problem in that a circuit element or structure is damaged if a wafer is heated to a high temperature of 800° C. to 900° C. as mentioned above. In order to solve such a problem, a CVD (chemical vapor deposition) is performed by using a plasma at a temperature in a low-temperature range such as, for example, 300° C. which is not so high.
FIG. 1 is an illustration of a structure of a conventional apparatus that performs the above-mentioned plasma CVD. First, a lower electrode unit 4, which also serves as a placement table, is situated in a process chamber 2 in which a vacuum can be created. A heater unit 6 such as a sheath heater is embedded in the lower electrode unit 4 in an insulated state. Specifically, the above-mentioned heater unit 6 is embedded by being cast into an aluminum material or the like. Additionally, an electrostatic chuck 8, which is made of ceramics, is provided on an upper surface of the lower electrode unit 4, which is made of aluminum, by being bonded by brazing and the like, the electrostatic chuck being formed by embedding an electrostatic chuck electrode in a ceramics material. The semiconductor wafer W is held on the electrostatic chuck 8 by an electrostatic attracting force.
Additionally, a cooling block 12 having a cooling Jacket 10 therein is provided in a lower portion of the above-mentioned lower electrode unit 4. The wafer W is maintained at an optimum temperature by controlling the above-mentioned cooling jacket 10 and the heater unit 6.
Since a heat transfer space 14, which is a small gap, is formed between the lower electrode unit 4 which decreases the heat transfer efficiency, an attempt is made to improve the efficiency of heat transfer by sealing the heat transfer space 14 by a seal member 16 such as an O-ring and introducing a heat-transfer gas, which is an inert gas such as Ar gas, He gas or nitrogen gas.
Additionally. An upper electrode unit 18 is provided on the ceiling of the process chamber 2, the upper electrode unit being positioned to face the above-mentioned lower electrode unit 4. A heater unit 20 such as a sheath heater is also embedded in the upper electrode unit 18 by being cast into an aluminum material or the like. Additionally, a high-frequency source 22 is connected to the upper electrode unit 18 so as to apply a high-frequency voltage for generating a plasma, and a predetermined process is applied to the wafer W by generating a plasma between the upper electrode unit 18 and the lower electrode unit 4.
In a case in which a process temperature of the semiconductor wafer is relatively low, for example, when the process temperature is lower than about 200° C., an influence of the process temperature to a member provided in the process chamber 2 is not large. However, in order to increase a film deposition rate or improve a film quality in a film deposition process for example, there is a case in which the process temperature is increased to a temperature greater than 200° C., that is, a temperature ranging from 350° C. to 500° C. in a range in which an element or a construction in a lower layer is not damaged.
In such a high temperature range, there is a problem in that a sealed gas leaks due to deterioration of the sealing characteristic of the sealing member 16 such as an O-ring sealing the heat transfer space 14 due to a thermal degradation. If the sealing characteristic of the sealing member 16 is deteriorated, the inert gas sealed in the heat transfer space 14 flows out, which results in deterioration of the efficiency of heat transfer. As a result, the accuracy of control of the temperature of the wafer W may be decreased, or a film deposition gas in the process chamber 2 may be diluted by the heat transfer gas, for example, in a film deposition process. In order to prevent such as problem, a flow rate of the film deposition gas must be increased more than a stoichiometric ratio, and, thus, there is a problem in that consumption of the film deposition gas is increased.
Additionally, since a pressure sensor cannot be provided to the heat-transfer space 14, which is heated to a high temperature, a pressure of the heat-transfer gas supply to the heat transfer space 14 is monitored by a supply source so as to control the supply pressure to become appropriate. However, in such a structure, a pressure in the area to be controlled is not directly detected, the controllability of the gas pressure must be deteriorated.
It should be noted that the present inventor suggested, in Japanese Laid-Open Patent Application No. 6-232082, a sealing structure for performing a process in a low-temperature state, which is a sealing structure under an ultra low-temperature environment such as a cooling device, which performs cooling by using liquefied nitrogen.